1. Field of the Invention
The present invention relates to battery-charging systems for electrical equipment. More particularly, the present invention relates to a battery-charging system that includes an electric power tool operating on rechargeable internal batteries and a battery charger for charging the internal batteries of the electric power tool.
2. Description of the Related Art
One type of conventional rechargeable electric power tool incorporates a detachable battery pack mounted in the lower end of the handle thereof. When the battery pack needs to be recharged, it is detached from the handle of the tool and set on a separate charger. After the charging is completed, the battery pack is mounted back in the handle to resume operation. If an electric power tool operating on a detachable battery pack is used for extended periods, for example, on a production or assembly line of an automobile plant, an auxiliary battery pack is set in a charger for recharging. When the pack mounted in the tool is discharged, the operator replaces it with the one recharged by the charger and sets the discharged battery pack on the charger for recharging.
Battery packs used for the above-described purpose are generally designed to maximize their capacity and thus the operating time of the tool. This tends to increase the size and weight of the packs, which in turn places an excessive physical strain on the operators and reduces the operability of the tools and work efficiency. This tendency is particularly pronounced when such large and heavy battery packs are used on assembly lines for an extended period; the operability of the tools may be severely affected so as to significantly reduce the productivity of the plant. In addition, loss of time by replacing discharged battery packs has been a significant factor that reduces work efficiency.
Furthermore, when bolts and screws must be tightened to specific torque, electric power tools of the above-described type often fail to fulfill the task, as the operators cannot ascertain the charge level of the battery packs.
Chargers used for such battery packs continue to supply charging current even after the battery packs are fully charged, therefore placing the batteries or cells in the pack under heavy load and reducing the charge efficiency.